BitTorrent is currently one of the most popular methods of distributing large files over the Internet. For a given file, the BitTorrent protocol embodies four main roles: an initial seeder, new seeders, a tracker, and peers. Initial seeders, new seeders, and peers are all transient clients; trackers are typically web servers. The initial seeder is the source of the file, and operates by dividing a file into small pieces, creating a metadata description of the file and sending this description to the tracker. Peers discover this file metadata description, usually as a .torrent file, through an out-of-band mechanism (e.g., a web page) and then begin looking for pieces of the file. Peers contact a central tracker to bootstrap their knowledge of other peers and seeds, and the tracker returns a randomized subset of other peers and seeds. Initially, only the initial seeder has pieces of a file, but soon peers are able to exchange missing pieces with each other. Once a peer acquires all of the pieces of a file, it becomes a new seeder. This collection of clients actively sharing a file is called a swarm.
BitTorrent client applications, however, generally are only able to access the file identified by the file metadata description (e.g., a .torrent file). Thus, accessing different files requires a peer to discover different corresponding file metadata descriptions (e.g., .torrent files). Without having a file metadata description readily accessible, content is otherwise unable to be discovered.